Hydrologic (Water) Cycle: Make a Terrarium

All of the water on the earth is in constant motion. Water falls to the earth as rain and then evaporates back up into the air making clouds. Then the water falls back down to earth again as rain. This cycle is call the hydrologic or water cycle.

To see how the hydrologic cycle works you can make your own little model of the earth in a terrarium. A terrarium is a little garden inside a sealed container.

What You Need:

a Clear Plastic or Glass Container With a Lid

Stones

Soil

Plants

Water

Little Toys for Decoration (optional)

When you poor water into your terrarium that is the beginning of the water cycle. You essentially have made it rain in your little glass world. When you set your terrarium in the sun the water inside the terrarium heats up and turns into water vapor in the air. This is called evaporation. When the water cools back down, it turns back into a liquid. You will see condensation – water droplets – sticking to the lid of your terrarium. If the drops get large enough, they will roll down the sides of the container or fall from the lid – rain!

The close-up on the left shows the condensation that began to form on the inside of the jar after only 1 hour sitting in the sun.

If there is too much water just open the lid and let some of the water evaporate. If your plants look wilted or dry, try adding a little more water. It might take some trial and error to get the amount of water needed just right.

Here are some websites and books that give you step by step directions for making a terrarium:

Science Experiment Idea: Make three identical terrariums. You have to use the same kind of container, the same amount of soil & the same plants. Make your variable (the thing you are going to test) the amount of water you put into the terrariums. Measure a different amount of water into each terrarium. Close the lids and watch the terrariums over several days to see which amount of water made the best environment for your plants. A terrarium with too little water will have dry plants. A terrarium with too much water will have plants with yellow leaves and maybe even mold growing on the soil!

Words to Know:

Terrarium- A clear container with a lid used for growing plants.Hydrologic (Water) Cycle – The movement of water from liquid to gas (evaporation) and from gas to liquid (precipitation).Condensation – Water vapor cooling off and changing to liquid water.Evaporation – Liquid water heating up and changing to water vapor.Precipitation – Rain, snow, or hail.